Hfq is a crucial regulator of succinate mediated catabolite repression of mineral phosphate solubilization in Acinetobacter sp. SK2

The PGPR Acinetobacter sp. SK2 enhances plant growth by solubilizing mineral phosphate via gluconate production. The presence of preferred carbon source-succinate, causes CCR of MPS. This study aimed to investigate the role of global regulator Hfq in succinate mediated catabolite repression of MPS in Acinetobacter sp. SK2. Insertional inactivation mutants of hfq were generated and the phenotypic analysis revealed altered growth pattern, ~70% derepression of MPS and ~19.7 mM gluconate production under repression condition compared to wild type strain. Complementation of the mutant with functional hfq gene restored the wild type phenotype indicating crucial role of Hfq in SMCR. These results demonstrate that Hfq likely mediates repression through post-transcriptional regulation of the genes involved in glucose utilization. The genes gdhA and gdhB , encoding glucose dehydrogenase enzymes mGDH and sGDH, respectively, were downregulated in glucose+succinate grown wild type, whereas the expression of these genes in hfq – strain was comparable to WT–G. The hfq – strain showed significant difference in mGDH (and sGDH) activity under repression condition as compared to WT viz. hfq – –GS mGDH activity was ~80% that of WT–G. The WT and mutant strains were studied for other PGP traits such as production of ammonia, HCN, Siderophore, IAA, etc., solubilization of Zn, K, and Organic P solubilization (via phytase). The WT and mutant strains were applied to plants Vigna radiata and Cicer aeriatinum in pot experiment set-up, where the inoculated plants showed better growth w.r.t. uninoculated and growth parameters of plants inoculated with hfq – were overall superior. • Hfq inactivation leads to derepressed MPS and gluconate production. • Hfq might be causing post-transcriptional regulation of mGDH and sGDH. • Hfq complementation reverted the mutant strain to WT phenotype of SMCR. • First study showing regulatory influence of Hfq on MPS in Acinetobacter sp. SK2.